Rubber thread and method of making same



June 1940. G. s. VAN VOORHIS' RUBBER THREAD AND METHOD OF MAKING SAMEFiled March 23, 1938 Patented June 4, 1940 RUBBER THREAD AND METHOD OFMAKING SAME Georges S. Van Voorhis, Northampton, Mass., assignor toUnited Elastic Corporation, Easthampton, Mass., a corporation ofMassachusetts Application March 23, 1938, Serial No. 197,655

4 Claims.

This invention relates to rubber threads and methods of making the same.It is more especially concerned with covered rubber thread and with themanufacture of this material.

Such thread is used extensively in the manufacture of a great variety ofelastic products, particularly articles of wearing apparel and parts ofsuch articles. When the processes of making products of this naturerequire sewing or stitching operations, it .is a common experience tofind that the needle of the sewing machine has cut one or more of therubber threads. While such a cut may not completely sever the thread,it-is the usual experience that when a thread has been nicked by aneedle, or in any other manner, it will thereafter tear relativelyeasily at the nicked point and will break if subjected'to any greatamount of strain. When this happens the ends of the rubber core of thethread draw back into the covering, and the difference in elasticitybetween this part of the fabric and adjacent areas produces a flaw inthe goods which either makes them unsaleable, or greatly reduces theirsaleability.

With a view to overcomingrthis difiiculty, it has been customaryheretofore to make the rubher core of a covered rubber thread of severalindependent strands. However, unless great care is taken in themanufacture of such a thread,

and sometimes in spite of such care, it is found that the thread has atendency to twist or will not lie straight. Sometimes this is due to atwisted core and often, also to differences in the initial tensionapplied to the threads during the covering operation. These are seriousobjections in the manufacture of most elastic webbings since animportant requirement is that they must lie flat and smooth. 7

The present invention is especially concerned with the foregoingconditions and the problems presented by them. It aims to produce arubber thread which will be relatively immune to the effects of needlecuts, which will lie smooth and J fiat, and which can be manufacturedeconomiwith which the method of this'invention may conveniently beperformed; and

Fig. 2 is a side view showing a covered rubber thread made in accordancewith this invention, the parts being separated at one end in orderbetter to show the construction.

Figure 1 of the drawing shows a typical arrangement for covering therubber core C to produce a covered rubber thread. It comprises upper andlower covering heads, indicated in general at 2 and 3, the two beingarranged in vertical alinement with each other. The lower head comprisesa rotary support 4 on which a spool, cop, or other thread body 5 ismounted, and includes a pulley 6 by means of which the head may berevolved about a vertical axis from any convenient source of power. Thisentire structure is provided with a central bore or tube, the lower endof which is shown at I, through which the rubber core C to be covered isfed upwardly. The thread T unwound from the spool or cop 5 is ledthrough a thread guiding eye in the outer end of a flyer 8, and fromthere to the core C where it is wound around this core as the latter isfed upwardly through the head.

The upper head 2 is of the same construction, and corresponding partsare indicated by. the same, by primed, numerals. From the upper head thecovered thread travels over a takeup roll I and goes thence to a spooll2 on which it is wound.

This arrangement is like that commonly used in this industry so that nodetailed construction of it is necessary.

According to the present invention, the rubber core, instead of beingsupplied to the covering mechanism in the form of a thread, is broughtto it in the form of a fiat tape I3. It is fed to. the head between,upper and lower feed rolls l4 and I which are positively connected withthe takeoff roll l0 so that the speed of the latter bears a definite andfixed ratio to the delivery speed of the rolls l4 and i5. This ratio ismade such that the, rubber core is held in a stretched and elongatedcondition continuously while it passes simply a single fold or curve inthe middle, and

the free edges will be bent somewhat toward each other. It ispreferable, however, to use a tape of such dimensions that it will befolded or curved longitudinally into a true tubular form with the freeedges in abutting relationship to each other. If the tape is wide enoughthe edges obviously will be overlapped more or less, one upon the other.Since the particular form which it will take depends upon the width ofthe tape at the time the thread is wrapped around it and this width, inturn, will depend to some degree upon the extent to which it isstretched at that time. these various curved forms will be hereinafterreferred to as approximately tubular forms. The covering thread orthreads thereafter hold the tape in this form or condition.Subsequently, as the rubber core is fed through the upper head 2, one ormore other threads are wound around it in a reverse direction to that inwhich 131."; first thread or threads are wound. It may here be notedthat while a single thread is shown at T and T in Figs. 1 and 2, a morecommon arrangement is to wind two or three strands of threadsimultaneously around the core at each covering point.

. Frequently a non-elastic stretch-limiting thread, such as an ordinarycotton thread, of suitable size, is included in the rubber core, andsuch a thread is shown at l6, Fig. 1, as it unwinds from the'supplyspool I1 and is fed over the guide roll Hi, this thread meeting therubber tape I3 as the latter is guided around the roll 20. The use ofsuch a thread in this process is of advantage in affording a centralform around which the tape is folded in the manner above described.Subsequently, when the tension on the finished thread is removed, itcontracts longitudinally to a degree depending upon the tensionmaintained in the core during the covering operation, and depending,also, to some degree, upon the nature of the covering and, consequently,the degree to which it permits the thread to contract, and during suchcontraction the stretch-limiting thread.

or so-called gut thread, I6, is gathered or puckered more or 'lesswithin its rubber covering. Also, as the core contracts longitudinally,it expands laterally and this fact modifies to some degree the shapewhich it takes inside the covering. In the absence of a gut thread therubber substantially fills the space which would be occupied by such athread if it were used.

While the tape l3 may consist of a single piece .of rubber, I prefer touse a tape made substanby the inherent adhesion of the rubber andvulcanized in this condition, but the degree of adhesion is reduced andcontrolled by the presence of a limited amount of talc, or some otherdry separating substance, between the threads, so that while the threadsofier considerable. resistance to separation from each other,nevertheless they are not united into an integral. structure. v

When a needle is forced through a thread made in this manner, it israrely that it cuts one of the strands. The usual effect seems to bethat the needle separates the individual strands and breaks the bonduniting them sufficiently to allow the needle to pass through.Apparently the thread more or less dodges the needle or, in other words,the needle finds the weakest place in the tape, which is the line ofbinding between adjacent strands. However, if a strand should be cut, itadheres to the other uninjured threads with sufiicient strength toprevent them from drawing back into the covering and thus producing aflaw in the goods in the manner above described. it

Whether, however, the rubber core is made from an integral tape, or ofone composed of a series of threads or strands adhesively united to eachother, the method above described provides an economical process ofmaking covered rubber thread. It requires no operations additional tothose necessarily used in making such a thread by the usual processes,and it lends itself conveniently to the manufacture of threads havingcores of different gages. For example, these thin tapes canbe made ofextremely thin thicknesses, even down to a hundredth of an inch.Consequently, the gage of a core made of tape of this thickness willdepend upon the width of the tape. Thus the desired flexibility in themanufacture of a product of this character is easily obtainable.

A further advantage of this method is that it is easy to feed the tapeto the covering instrumentalities without twisting it. In fact, it wouldbe more difficult to feed it otherwise. Consequently, the objectionablecharacteristics re sulting from a twisted core are readily avoided.

When the core consists of, or includes, a tape composed of a series ofrubber strands adhesively united to each other, as above described, thedifficulty heretofore experienced in making covered rubber thread with a,core composed of a plurality of independent rubber threads is avoidedbecause the tape, being a unitary structure. all the threads or strandsare subjected to the same degree of tension. Also, in this constructionthe fact that the threads composing the tape are adhesively united toeach other practically eliminates the difficulty heretofore experiencedwith the breakage of rubber threads, A contributing factor to thisresult is the fact that the tape tends constantly to spring into itsoriginal flat form, this tendency being additional to its inherentdisposition to expand laterally.

Thus the invention materially reduces the difficulties previouslydescribed in using rubber threads of the orthodox types. Y

Having thus described my invention, what I desire to claim as new is:

1. A rubber thread comprising a strip rubber tape composed of a. seriesof parallel rubber threads adhesively bonded to each other in a side byside relationship but not integrally united. said tape being curvedlongitudinally into an ap proximately tubular form, and means holding itin said form;

2. A rubber thread comprising a strip of rubber tape composed of aseries of parallel rubber threads bonded directly to each other by acontrolled adhesion which holds them releasably in said relationshipwithout integrally uniting them, but by a union offering substantialresistance to the separation of the threads, said tape being curvedlongitudinally into an approximately tubular form, and a covering ofthread wound around said tape and holding it in said form.

3. A covered rubber thread comprising a strip of rubber tape composed ofa series of parallel rubber threads united to each other in a parallelside by Side relationship by a controlled adhesion, a central stretchlimiting thread, said tape being curved longitudinally around saidstretch-limiting thread, and acovering of thread ams-p22 3 side and intocontact with the flat race 0! said tape, and winding one or morecovering threads around said tape while it is being so fed and therebycurving the tape around the first thread into an approximately tubularform and binding 5 it in said form by said covering thread or threads.

GEORGE S. V AN VOORHIS.

